/*
 * Copyright (C) 2008 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.common.collect;

import com.google.common.annotations.GwtCompatible;
import com.google.common.primitives.Ints;

import javax.annotation.CheckForNull;

/**
 * Static methods for implementing hash-based collections.
 *
 * @author Kevin Bourrillion
 * @author Jesse Wilson
 * @author Austin Appleby
 */
@GwtCompatible
@ElementTypesAreNonnullByDefault
final class Hashing
{
    private Hashing()
    {
    }

    /*
     * These should be ints, but we need to use longs to force GWT to do the multiplications with
     * enough precision.
     */
    private static final long C1 = 0xcc9e2d51;
    private static final long C2 = 0x1b873593;

    /*
     * This method was rewritten in Java from an intermediate step of the Murmur hash function in
     * http://code.google.com/p/smhasher/source/browse/trunk/MurmurHash3.cpp, which contained the
     * following header:
     *
     * MurmurHash3 was written by Austin Appleby, and is placed in the public domain. The author
     * hereby disclaims copyright to this source code.
     */
    static int smear(int hashCode)
    {
        return (int) (C2 * Integer.rotateLeft((int) (hashCode * C1), 15));
    }

    static int smearedHash(@CheckForNull Object o)
    {
        return smear((o == null) ? 0 : o.hashCode());
    }

    private static final int MAX_TABLE_SIZE = Ints.MAX_POWER_OF_TWO;

    static int closedTableSize(int expectedEntries, double loadFactor)
    {
        // Get the recommended table size.
        // Round down to the nearest power of 2.
        expectedEntries = Math.max(expectedEntries, 2);
        int tableSize = Integer.highestOneBit(expectedEntries);
        // Check to make sure that we will not exceed the maximum load factor.
        if (expectedEntries > (int) (loadFactor * tableSize))
        {
            tableSize <<= 1;
            return (tableSize > 0) ? tableSize : MAX_TABLE_SIZE;
        }
        return tableSize;
    }

    static boolean needsResizing(int size, int tableSize, double loadFactor)
    {
        return size > loadFactor * tableSize && tableSize < MAX_TABLE_SIZE;
    }
}
